Sensitivity of the superconducting state in thin films

Abstract

For more than two decades, there have been reports on an unexpected metallic state separating the established superconducting and insulating phases of thin-film superconductors. To date, no theoretical explanation has been able to fully capture the existence of such a state for the large variety of superconductors exhibiting it. Here, we show that for two very different thin-film superconductors, amorphous indium oxide and a single crystal of 2H-NbSe2, this metallic state can be eliminated by adequately filtering external radiation. Our results show that the appearance of temperature-independent, metallic-like transport at low temperatures is sufficiently described by the extreme sensitivity of these superconducting films to external perturbations. We relate this sensitivity to the theoretical observation that, in two dimensions, superconductivity is only marginally stable.

Quantum breakdown of superconductivity in low-dimensional materials

“…Martinis and coworkers 73,97 have addressed this subject in the context of macroscopic quantum tunneling. Additionally, the thermal blackbody-radiation has been found to contribute significantly to the performance of superconducting quantum circuits 98 A reminder of the importance of the sensitivity to environmental radiation for materialsresearch was shown in recent experiments by Tamir et al 10 , which showed it in the resistive transition of a:InO, but also of a crystalline 2D superconductor, H2-NbSe 2 . A similar dependence was found recently by Dutta et al 11 in the onset of resistance in the vortex state of a-MoGe-films.…”

“…• The experimentally observed high sensitivity 10,11 to radio-wave interference, as known for Josephsonjunctions of SIS and SNS-type 73 , calls for an analysis of the effect of microwaves on the study of superconducting materials, which are expected to be spatially inhomogeneous. Both the common Josephson-response due to a local voltage difference, affecting the local phase-differences, should be considered as well as the non-equilibrium effects, which change the Josephson-coupling.…”

Superconducting phase transitions in disordered NbTiN films

“…The direct disorder-driven SIT is observed, for example, in indium oxide InO x [8][9][10] and titanium nitride TiN 11,12 films. At present, the interrelation between these mechanisms as well as the nature of the possible intermediate Bose metal [13][14][15][16] still are not completely understood and are intensively debated 2,17 .…”

Free at last: Bose metal uncaged

“…A direct attack on the refrigeration problem came from the experiments that showed the metallic state in amorphous InO x [3] and crystalline 2H-NbSe 2 [9] were artifacts [10] as they vanished by eliminating all sources of electromagnetic radiation. Yang, et al [6]employed this now standard filtering scheme to directly address what is carrying the current in the metallic phase.…”